1. Field of the Invention
This invention relates broadly to devices for purifying water and other fluids and has particular reference to an improved removably mounted ultraviolet lamp assembly for such devices.
2. Description of the Prior Art
Purifying devices for water and other fluid have been known heretofore in which the fluid passes first through a filter to filter out any solids and then passes a source of ultraviolet rays effective to destroy microorganisms, spores, and the like, which pass through the filter. Generally, this is accomplished by passing the fluid over the envelope of an ultraviolet lamp or over a quartz jacket surrounding the lamp.
It is found that in such known devices, during operation of the lamp, calcium and other colloidal matter which passes through the filter tends to coat the lamp envelope or other transparent medium separating the fluid from the lamp, thus building up a scale or other contamination which reduces the intensity of the ultraviolet rays and therefore reduces the effectiveness of the lamp in destroying the microorganisms, etc. This attenuation of the ultraviolet transmission is not easily detected by inspection and therefore the device must be frequently disassembled and the ultraviolet lamp or quartz jacket cleaned to insure effective sterilization.
In some of the known devices, attempts have been made to maintain the efficiency by employing mechanical scrubbers or scrapers to periodically remove the accumulated scale and other contamination, but these add to the complexity and cost of the device and have not proved entirely satisfactory.
Until rather recently, these prior fluid purification devices have in general comprised separate units for first filtering and then sterilizing the fluids. Such units are relatively bulky, complicated and difficult to disassemble for cleaning, inspection and replacement of the ultraviolet lamps, filters and other components.
As will be observed from U.S. Pat. No. 3,551,091, the patentee, L. P. Veloz, attempted to overcome the disadvantages attending the use of separate filtering and sterilizing units by providing a combination water filter and sterilizer within a single housing, and wherein a removable filter surrounds an ultraviolet lamp which is shielded against the fluid pressure by means of a surrounding quartz tube. Thus, it appears that while the embodiment of this patent did produce a more compact and simplified device, it did not solve the problem of scale and contamination buildup which tended to reduce the irradiating efficiency of the device during use.
Other attempts were also made to improve fluid sterilizing units, as disclosed for example in U.S. Pat. No. 3,700,406 to A. Landry, by utilizing fluorinated ethylene propylene plastic, commercially known as Teflon F.E.P., and which has excellent non-stick qualities, is non-contaminating, and will not deteriorate in the presence of ultraviolet light. In this patent it has been proposed to use such material for piping to carry the fluid past a source of ultraviolet light. However, attempts to utilize such material for piping has, in the main, been unsuccessful because of its high imperviousness to ultraviolet rays, when of sufficient thickness to withstand the normally used fluid pressures. For example, considering quartz to have an ultraviolet ray transmission factor of 100%, a sheet or the like of Teflon F.E.P. 0.010 inches thick will reduce U.V. transmission to 25%, although a sheet of Teflon F.E.P. 0.002 inches thick will transmit 75%. It will therefore be apparent that such material could not be used as piping or other means for conveying fluids under the pressures usually employed in connection with fluid purification systems, since it would require a thickness such that ultraviolet transmission would be unduly attenuated.
In its broad aspects, the present invention overcomes the above noted problems and disadvantages of the prior art devices by utilizing a unique ultraviolet lamp, the outer surface of which is covered with a thin film of a material having non-stick characteristics with respect to the fluid being treated, such as fluorinated ethylene propylene. The film is of such thinness as to have a high degree of transmission for the ultraviolet rays, and yet will withstand the fluid pressure in an associated flow channel because of its intimate engagement with the outer surface of the ultraviolet lamp envelope. With this arrangement scale and contamination around the lamp are substantially reduced, and efficiency of operation maintained over long periods of use.